1. Field of the Invention
Subject of the invention is a fastener for closing and sealing ends of pipes, for example plastic pipes, subjected to the action of internal pressure and tested in suitable apparatus in which a pipe segment is filled with water and subsequently an increased pressure is establisched in the pipe, its value corresponding with the required stress in the pipe wall.
2. Description of the Related Art
From the Polish Patent Specification No. 145005 and from the European Patent Application, No. of Publication No. EP-0204270 there is known a hydraulically closed fastener composed of two main parts, namely a cover and a clamp. These two parts are screwed together and thus they enclose a space inside which there are placed a conical elastic sealing and a slidable element. When the fastener has been placed on the pipe end, then the conical ring is at the outside diameter of the pipe under test and the elastic sealing on its end face.
In the cover of the fastener there is located a valve for supplying water to the space between the cover and the movable element. In the cover there is cut out axially a hole for introducing water to the interior of the pipe.
The lower portion of the movable element has a conical surface which cooperates with the conical surface of the elastic ring.
When water has been supplied to the fastener and an increased pressure established in the pipe under test, then the movable element slides in the direction of the end face of the pipe, thus clamping the elastic sealing and the elastic ring. Thus, the fastener becomes fastened on the pipe end, water is supplied into the pipe, an increased pressure is established in it and the relevant test of the internal pressure resistance of the pipe can be carried out.
A drawback of this fastener is the necessity of a continuous supplying of its elements with water to keep the fastener clamped on the pipe during the whole duration of the test, which sometimes reaches 1,000 hours. Moreover, when disassembling the fastener it is often difficult to separate the cover from the clamp due to the seizure of the threads and to the expansion of the conical ring.
From among other designs, a fastener for closing the pipe ends is also known from the Patent Specification of the USSR No. 977968.
This fastener has a cover screwed together with a clamp: inside the clamp there is located a conical clamping ring whereas inside the cover there is a movable conical pin which slides under the action of pressure and seals the pipe end on its internal surface. This surface has been bevelled and against this bevelled surface edge the pin is pressed with its conical surface.
This fastener is suitable both for closing steel pipes and plastic pipes, but only for tests carried out at room temperature, under low pressures and during short periods of time. When these conditions are not met, the pipe material would be destroyed even under low loads applied to it.
A fastener for closing and sealing pipes is also known from the patent Specification of U.S. Pat. No. 3,434,337. In the frame of this fastener there are located several tens of parts, from among which an essential importance for comparing it with the fastener of the present invention have conical elements clamped with a flat element moving under the action of increased pressure from the medium supplied.
This flat element has the shape of a disc with hole which is situated axially on the pipe. Its movement causes a displacement of segments which with their conical surfaces act on the conical surfaces on the next segments and thus clamp them on the pipe. Sealing is realized here by means of a circular packing of the "U"-type situated with its open face to the supplied medium between the external surface of the pipe and internal surface of the sleeve.
This attachment is characterized by a high complexity of its design, is composed of a large number of parts and has considerable dimensions and weight. It makes no separate fastener which can be fastened on the pipe end and placed together with the pipe section in the water tank for the test apparatus, but it makes an integral part of such apparatus.